Transactions of the Korean Society of Mechanical Engineers A (대한기계학회논문집A)

The Korean Society of Mechanical Engineers (대한기계학회)
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Flaw Detection in Pipe-Welded Zone by Using Wavelet Transform and SH-EMAT

웨이브렛 변환과 SH-EMAT을 이용한 배관 용접부 결함 검출

  • Lee, Jin-Hyuk (Graduate School of Energy and Environment, Seoul Nat'l Univ. of Science and Technology) ;
  • Kim, Dae-Hyun (Dept. of Mechanical & Automotive Engineering, Seoul Nat'l Univ. of Science and Technology)
  • 이진혁 (서울과학기술대학교 에너지환경대학원) ;
  • 김대현 (서울과학기술대학교 기계.자동차공학과)
  • Received : 2012.05.17
  • Accepted : 2012.09.05
  • Published : 2012.12.01
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Abstract

Pipe structures contain many welded zones, and ultrasonic tests are increasingly being performed by using automated testing devices in order to evaluate the weld integrity. An electromagnetic acoustic transducer (EMAT) is a noncontact transducer that can transmit or receive ultrasonic waves without a couplant. Furthermore, it can easily generate specific guided waves such as SH (shear horizontal) or Lamb waves by altering the design of the coil and magnet. Therefore, an EMAT should be useful for application to an automated ultrasonic inspection system. In this study, SH waves generated using an EMAT were applied to inspect the pipe-weld zone. To analyze the specific SH mode (SH0) from the SH wave signals, wavelet transform was applied. It was found that flaws could be detected precisely because the intensity of the $SH_0$ mode-frequency, which is analyzed by using wavelet transform, is proportional to the length of the flaw.

배관설비는 용접이음으로 많은 부분이 구성되어 있으며, 이러한 배관 용접부의 건전성 평가를 위한 초음파 검사 시스템의 자동화 요구가 증대하고 있다. 전자기초음파탐촉자(Electromagnetic Acoustic Transducer; EMAT)는 비접촉 방식으로 초음파를 송 수신할 수 있고 다양한 초음파 모드의 발생이 가능하여 초음파 자동화 시스템 구축에 매우 유용하다. 본 연구에서는 수평횡파(Shear Horizontal wave; SH-wave) EMAT를 적용하여 배관의 용접부에 존재하는 결함의 검출을 수행하였다. 이때 수평횡파의 특정 모드($SH_0$)의 신호해석을 위해 웨이브렛 변환(Wavelet Transform)을 이용한 신호의 시간-주파수 분석을 수행 하였다. 웨이브렛 변환으로 해석된 SH0 모드 주파수의 반사 신호강도가 결함의 길이와 선형적 관계를 나타내어 효과적으로 용접부 결함 검출이 가능하였다.

Keywords

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